I have a slop sink in the basement tied into a 4" stack through a cleanout with a nice fiting and 1.5" PVC to a P trap and to the sink. There is no other drains in the basement, two other stacks that are not near by and I know I am suppose to have a vent but the sink works great. How could I vent this and if I don't what are the issues I might have other than the possibility of the larger drains pulling the water out of my trap and allowing sewer gases in? I check it often and I have none yet. I didn't install it and hate to loose the sink. LM in NJ